8068
Journal of the American Chemical Society
(21) J. P. Devlin and I. C. Hiatsune, Spectrochim. Acta, 17, 206 (1961). (22) T. L. Cottrel, "The Strength of the Chemical Bond", 2nd ed.. Butterworths, London, 1958. (23) M. Lister and L. E. Sutton, Trans. Faraday SOC., 35, 495 (1939). (24) P. A. Giguere and D. Chin, Can. J. Chem., 39, 1216 (1961). (25) J. Sheridan and W. Gordy, Phys. Rev., 79, 513 (1950). (26) F. W. Levine and S. Abramowitz, J. Chem. Phys., 48, 2562 (1966). (27) C. B. Colburn and A. Kennedy, J. Chem. Phys., 35, 1892 (1961). (28) M. L. Unland, J. H. Lucher, and J. R. Van Wazer, J. Chem. Phys., 50,3214 (1969). (29) Y. Morino and S. Saito, J. Mol. Spectrosc., 19, 435 (1966). (30) J. W. Nebgen, F. I. Metz, and W. B. Rose, J. Mol. Spectrosc., 21, 99 (1966). (31) J. Troe, H. Wagner, and G. Weden. 2.Phys. Chem. (Frankfurt a m Main), 56, 238 (1967). (32) L. Pierce, R. Jackson, and N. DiCanni, J. Chem. Phys., 35, 2240 (1961). (33) L. Pauling and L. 0. Brockway, J. Am. Chem. Soc., 59, 13 (1937). (34) J. Shamir, D. Yellin, and H. Claassen, lsr. J. Chem., 12, 1015 (1974). (35) R. H. Miller. D. L. Bernitt, and I. C. Hiatsune, Spectrochim. Acta, Part A, 23, 223 (1967). (36) (a) F. P. Deodati and L. S. Bartell, J. Mol. Struct., 8, 395 (1971); (b) R. R. Smardzewski and W. B. Fox, J. Fluorine Chem., 6, 417 (1975). (37) J. Czamowski, E. Costellano, and H. J. Schumacher, Chem. Commun., 1255 (1968). (38) H. Kim, E. F. Pearson, and E. H. Appelman, J. Chem. Phys., 56, 1 (1972). (39) J. A. Goleb, H. H. Claassen, H. M. Studier, and E. H. Appelman, Spectrochim. Acta, Part A, 28, 65 (1972). (40) P. N. Nobel and G. C. Pimentel. Spectrochim. Acta, Part A, 24, 797 (1968). (41) S . L. Rock, E. F. Pearson. E. H. Appelman, C. L. Norris, and H. W. Flygare. J. Chem. Phys., 59, 3940 (1973). (42) E. W. Lawless and I. C. Smith, "Inorganic High Energy _.Oxidizers", Marcel Dekker, New York, N.Y., 1968. (43) K. R. Loos. G. T. Gaetschei, and V A. Camponile, J. Chem. Phys., 52,4418 (1970). (44) J. T. Malone and H. A. McGee. Jr., J. Phys. Chem., 69, 4338 (1965). (45) N. J. Lehmann. J. Mol. Soectrosc.. 7. 261 11961). (46) L Pauling, 'The Nature of the Chemical Bond", 3rd ed , Cornell University
/ 100.26 / December 20, 1978
Press, Ithaca, N.Y.. 1960. J. W. Linnett, J. Am. Chem. Soc., 83, 2643 (1961). R. D. Spratley and G. C. Pimentel, J. Am. Chem. Soc., 88, 2394 (1966). F. P. Billinaslev II. J. Chem. Phvs.. 62. 864 (1975). C. Petron&o: E. Scrocco, &d'J. Tomasi, J. &em. Phys., 48, 407 (1968). (51) S. D. Peyerimhoff and R. J. Buenker, Theor. Chim. Acta, 9, 103 (1967). (52) J. Peslak Jr., D. S. Klett, and C. W. David, J. Am. Chem. Soc., 93, 5001 (1971). (53) R. Ditchfieid, J. Dei Bene, and J. A. Pople, J. Am. Chem. Soc., 94, 4806 11972). (54) C.-Snyder and H. Basch, "Molecular Wavefunctions and Properties", Wilev. New York. N.Y.. 1972. (55) W. Sawodny and P. Pulay, J. Mol. Spectrosc., 51, 135 (1974). (56) D. P. Chong, F.G. Herring, and D. McWilliams, J. Nectron Spectrosc. Relat Phenom., 7, 445 (1975). (57) W. J. Hehre, R. F. Stewart, and J. A. Pople, J. Chem. Phys., 51,2657 (1969); W. J. Hehre, W. A . Lathan, D. Ditchfield. M. D. Newton, J. A. Pople, QCPE No. 10, 1973, p 236. (58) R. Ditchfield, W. J. Hehre. and J. A. Pople, J. Chem. Phys., 54, 724 (1971). (59) R. Ditchfield, W. J. Hehre, and J. A. Pople, J. Chem. Phys., 56, 2257 (1972). (60) P. G. Mezey and I. G. Csizmadia, Can. J. Chem., 55, 1181 (1977). (61) J. L. Whitten, J, Chem. Phys., 44, 359 (1966). (62) T. H. Dunning, Jr., J. Chem. Phys., 53, 2823 (1970). (63) T. H. Dunning, Jr., J. Chem. Phys., 55, 716(1971). (64) T. H. Dunning, Jr., and P. J. Hay in "Modern Theoretical Chemistry", Vol. 3. H. F. Schaefer 111, Ed., Plenum Press, New York, N.Y., 1977. (65) L. J. Lawlor, K . Vasudevan, and F. Grein, to be published. (66) P. C. Hariharan and J. A. Pople, Theor. Chim. Acta. 28, 213 (1973). (67) R. J. Buenker and S. D. Peyerimhoff, Theor. Chim. Acta, 35, 33 (1974). (68) R. J. Buenker and S. D. Peverimhoff. Theor. Chim. Acta. 39. 217 (1975). (69) R. J. Buenker and S. D. Peyerimhoff, Chem. Rev.. 74, 127 (1974) (70) P. G. Burton and 8. R. Markey, Aust. J. Chem., 30, 231 (1977). (71) J. Berkowitz and A. C. Wahl, Adv. Fluorine Chem., 7 (1973). 1721 S. Rothenbero and H. F Schaefer . ... Ill. ./. Am. Chem - - SOC. _ _ - 95. - -, -2095 --(1973) (47) (48) 149) (50j
i.
Paramagnetic Organometallic Compounds of the Early Transition Metals Stabilized by Chelating Benzyl and Phenyl Ligands Leo E. Manzer Contribution No. 2566 from the Central Research & Deoelopment Department, E . 1. du Pont de Nemours and Company, Experimental Sthtion, Wilmington, Delaware 19898. Receiued April 17, 1978
Abstract: The reactions of LiCH2C6H4-o-NMe2 and LiC6H4-o-CH2NMe2 with Cp2MCI ( M = Ti, V , Sc; C p = q5-C5H5),
CpTiCl2, CrCI3, and ScC13 led to the isolation of thermally stable, air-sensitive organometallic complexes whose stability is attributed to chelation. The reaction of CpTi(CsH4-o-CH2NMez)z with CO2 leads to elimination of 1 equiv of N,N-dimethylbenzylamine and incorporation of CO2 into the aromatic ring. The reaction of Cr(CH2C6Hd-o-NMe2)3 with COz gives a paramagnetic complex in which CO2 has inserted into only one Cr-C bond and with diketones to give (diketonate)Cr(CH2C6H4o-NMe2)2. The factors which contribute to the stabilization of paramagnetic organometallic compounds are discussed.
Introduction Thc vast majority of organometallic compounds are diaLittle effort has been directed toward the synthesis of paramagnetic organometallic compounds because of the reactivity and instability of these compounds. The use of bulky alkyl substituents3-' such as -CH2SiMe3, -CH(SiMe3)2, and -CMe3 has yielded some very interesting and stable complexes. Recent work in our as well as in others"-I2 has shown that considerable stabilization can be achieved by the use of chelating organic ligands. For example, Brintzingert3 studied the reactions of alkyl Grignard reagents with Cp2TiCl and found that the resulting paramagnetic compounds, CplTiRz-, were very reactive and unstable a t room temperature. In contrast, we foundi4that the chelating lithium reagents 0002-7863/78/1500-8068$01 .OO/O
Li(CH2)2PR2 reacted with Cp2TiC1,I5 a t room temperature, to give 1 as thermally stable, paramagnetic, crystalline solids. CpLTi/CH2\pR2
'!HC' 1
Similar compounds were isolated for vanadium and scandium. The stability of these complexes prompted us to examine, in greater detail, the stabilizing effect of chelating organic ligands. The work described in this paper is concerned with the preparation of compounds of the general types 2 and 3 (where M = Sc, Ti, V, and Cr; L = Cp, diketone; x = 0, 1,2; y = 1-3). 0 1978 American Chemical Society
Manzer
Organometallic Compounds of the Early Transition Metals
8069
Table 1. Electronic Spectra and Magnetic Moments for Paramagnetic Organometallic Complexes
coni pd ( I
solvent THF
Cp:Ti(C6HJCH?N Mel)
THF
Cr(p-r- BuCOH3CH2NMer)? C ~ T I ( C ~ H ~ CMe?)? H~W
TH F ChHsMe
Cr(CH&HJN
CH2CIr
C p 2 V ( C H ? C h H ~Me?) N
ChHsMe
Cp?Ti(CH&HAN Me?)
ChH5Me
CpTi(CH2ChHdNMer)?
C hH .S Me
C r ( DBM)(CH?ChHjNMe?)? Cr(acac)(CH?ChH4NMe?)? Cr(O?CCH~ChH~h’Me~)(CH?CO Me?): H~N
CHrCI2 ChHh ChHh
electronic spectrum wavelength nm
extinction coefficient
434 514 683 740 635 468 574 705 656 745 600 715 500 717 615 770 SI2 543 62 I
I83 I40 161 48 45 34 268 21 I 80 84 137 131 90 49 210 150 326 I07 214
magnetic moments solvent P?? ChHh
2.6
ChBh
I .7
ChHb ChHh
3.7 1.7
CHlCI?
3.6
ChH6
2.6
CbHo
1.7
ChHb
I .6
CH?CI? CHzCI? CH2C12
4. I 4. I 3.0
DBM = anion of diben7oylniethane: acac = anion of acetylacetone; C p = cyclopentndienide
Compounds of type 3 are known for copper,I6 cobalt,17 gold,I8 silver,19nickel,1° palladium,20 and platinum.20The caverage has now been extended to include chromium, titanium, vana-
3
2
dium, and scandium. Derivatives of the isoelectronic benzylchelated compound, 2, have been prepared for the first time and are described i n detail.
Results A. Preparation of the Organolithium Reagents. The complexes described below were prepared from the lithium reagents 4 and 5. The phenyllithium reagent has been prepared R I
h
CH,
T I
I Y
I .
I\
Me, 4
Me,
5
previously under a variety of condition^.^^.^^^^' We have found that the most satisfactory procedure is to add an equimolar amount of n-butyllithium to an ether solution of N,N-dimethylbenzylamine. After 24 h, the white pyrophoric reagent, 4 ( R = H), precipitates in essentially quantitative yield. It may then be filtered, washed with pentane, dried, and stored under a nitrogen atmosphere at room temperature. Starting with the substituted amine, 4 (R = -CMe3) was prepared in good yield following the method of Cope and G0ur1ey.I~ The benzyllithium reagent, 5, cannot be prepared in good yield from equimolar amounts of N,N-dimethyl-o-toluidine and n-butyllithium in refluxing hexane. However, in an ether/hexane mixture, 5 precipitated after 2 days a t room
temperature as a pale yellow, ether-free pyrophoric solid. It may be separated by filtration, washed with pentane, dried, and stored under nitrogen a t room temperature for several years without signs of decomposition. Metalation of the methyl group was confirmed by N M R and mass spectroscopy after deuterolysis which gave only Me2NC6H4CH2D. It is very soluble in tetrahydrofuran and insoluble in ether and hydrocarbon solvents. B. Preparation of Cyclopentadienyl Transition Metal Derivatives. The addition of l molar equiv of 4 (R = H) to a suspension of Cp2MC11-’( M = Ti, V, Sc) in ether gave an immediate precipitate of LiCI. After the solutions were stirred for a short time, they were filtered and the solvent was removed to give CpzM(ChH4-o-CH2NMez) as very air-sensitive, crystalline solids. The titanium and vanadium compounds are paramagnetic (Table 1) with magnetic moments (determined in solution2z) indicating one and two unpaired electrons per metal, respectively. Teuben et al.” have recently reported the preparations of the titanium and vanadium complexes as part of a study of the thermal stabilities of organometallic compounds. The addition of LiCH2C6Hd-o-NMez to a magnetically stirred suspension of CpzTiCl in ether, under a nitrogen atmosphere, gave a dark green solution from which Cp2Ti(CHzC6H4-o-NMel) was isolated as a dark green, very air-sensitive, crystalline solid. The magnetic moment, determined in benzene, was 1.7 p ~ Deuterolysis . of 2 gave oMe2NC6H4CH2D. Similarly, CpzV(CH2C6H4-o-NMeI) was obtained as a very air-sensitive, green-brown, crystalline solid from the reaction of 5 with CpzVCl in ether. In contrast to C ~ I T ~ C H I C which ~ H ~ decomposes ,~~ at room temperature, it may be stored a t room temperature for several days under nitrogen with no apparent decomposition. The vanadium complex is much less stable than the titanium complex and decomposes after several days a t room temperature under a nitrogen atmosphere. The ESR spectrum of CpzTi(CH2C6H4-o-NMez) is unusual in that it shows a doublet at g = 1.981 from coupling of the electron with one hydrogen atom ( ( a ) , ) = 5.1 G). The reason for the nonequivalence of the -CHz-hydrogens is not clear but it may be due to steric interactions.24 Green and Lucas15 tried to prepare, without success, monocyclopentadienyl compounds CpTiRz by the reaction of [CpTiC12]x26with the lithium or Grignard reagent of R. They
8070
Journal of the American Chemical Society
/ 100:26 / December 20, 1978
8
soluble in ether and may be recrystallized from hot hexane. The magnetic moment is consistent with a d3 electronic configuration.28 The scandium compound Sc(C6H4-o-CH2NMe~)~ was prepared from ScC13 and LiCbH4-o-CH2NMe2 in refluxing tetrahydrofuran and was obtained as a white, insoluble compound. Unlike the chromium analogue, it is pyrophoric in air and decomposes violently in CH2Cl2 and methanol. The addition of 3 equiv of LiCH2C6H4-o-NMe2 to a suspension of CrC13 in T H F gave an immediate reaction and a dark orange solution from which dark red crystals of 9 were
A
d
Figure 1. X-ray crystal structure of CpTi(CsHa-o-CHzNMe)2.
found that disproportionation occurred to give Ti( 11) and Ti(IV) compounds. In contrast, 2 equiv of 4 and 5 reacted smoothly with [CpTiCl2], in ether to give CpTi(CH2C6H4o-NMed2 and CpTi(CbH4-0-NMe2)2 as dark green, crystalline, very air-sensitive compounds. The magnetic moments of 1.6- 1.7 k g , which were determined in benzene, are consistent with a d' electronic configuration. Both of these compounds should be stored under nitrogen at
